Fluid pressure operated pipe cutting or milling apparatus with floating valve



F. A. H ESTER PERAT Dec. 6, 1955 I 2,725,936 FLUID PRESSURE 0 ED PIPECUTTING OR MILLING APPARATUS WITH FLOATING VALVE 2 Sheets-Sheet 1 FiledMarch 6, 1953 r M e 46 1T0 N v A/ sw m M if, H WM Q 1 CL A A. d 4 P vvfl fifl fl/W F B W 2 A f f 1% A? I in??? A U I I. 7.! A I Z m w m a Dec.6,. 1955 F. A. HESTER 2,725,936

FLUID PRESSURE OPERATED PIPE CUTTING OR MILLING APPARATUS WITH FLOATINGVALVE 2 Sheets-Sheet 2 Filed March 6, 1953 Fred A. Healer IN V EN TOR.4. Mull Jam A TTOFFNE Y6 United States Patent FLUID PRESSURE OPERATEDPIPE CUTTING OR MILLING APPARATUS WITH FLOATING VALVE Fred A. Hester,Houston, Tex. Application March 6, 1953, Serial No. 340,784 12 Claims.(Cl. 164-.8)

This invention relates to new and useful improvements in fluid pressureoperated pipe cutting or milling apparatus with floating valve.

The pipe cutting or milling apparatus of this invention is an improvedtool which is particularly adapted for cutting a longitudinal section orwindow in a well pipe or casing whereby the walls of the well boreexterior of the casing are exposed to permit subsequent sidetracking orsimilar operations. The casing milling tools previously known haveseveral main disadvantages, one of which is inadequate mud or drillingfluid circulation to the cutter knives during the milling-out operationwhich often results in failure of the knives or unsatisfactory cuttingor milling, particularly when any bridging of the formation occursduring the milling-out operation.

Another main disadvantage or deficiency in previously known casingmilling tools has been in their inability to permit the well fluid toby-pass through the tool and enter the drill pipe as the tool on saiddrill pipe is lowered within the well pipe. This deficiency materiallyaifects the speed of lowering the tool and often the lowering of thetool must be halted in order to equalize the fluid pressure interioriyand exteriorly of the tool.

Still another disadvantage or deficiency in the prior casing millingtools has been their lack of a means to permit adequate reversecirculation back through the tool from the casing. Reverse circulationmay be necessary to remove trash or debris which has collected in thetool during the lowering thereof. if such trash or debris is notremoved, the tool must be pulled full of the mud or well fluid which isslow and costly.

It is therefore an object of this invention to provide an improved pipeor casing milling tool which has pipe cutter knives actuatable by fluidpressure and which over- I comes the aforesaid disadvantages of theprior known casing milling tools. 7

An important object of this invention is to provide an improved pipe orcasing milling tool wherein a floating valve is provided in the toolwhich is adapted to be maintained closed during the cutting through ofthe casing or pipe with cutter knives on the tool and which is adaptedto be opened by a predetermined fluid pressure after the knives have cutthrough the casing or pipe so that ade: quate liquid or mud circulationcan be effected during the milling out of the longitudinal section orwindow in the casing or pipe to remove all cuttings and any bridging ofthe formation so as to prevent damage to the cutter knives and therebyavoid pulling the tool for repair or replacement of the knives.

Another object of this invention is to provide an improved pipe orcasing milling tool which is adapted to fill up with well fluidautomatically during the lowering thereof into the pipe or casing tothereby facilitate the speed of lowering of the tool.

Another object is to milling tool through lation can be efiected whichsufi'icient reverse liquid circuto remove any foreign objects in thetool plugging the same, whereby the tool can be cleared 2,725,936Patented Dec. 6, 1955 proved pipe or casing milling tool wherein amaximum fluid pressure is utilized for extending the cutter knife orknives while cutting through the pipe or casing and maximum liquid ormud circulation is obtained during the milling of a longitudinal sectionof the pipe or casing to remove cuttings as well as any bridging of theformation.

The construction designed to carry out the invention will be hereinafterdescribed together with other'features thereof.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, where in an example of the invention is shown,and wherein:

Figure 1 is an elevational view of the casing or pipe milling tool ofthis invention, illustrating its use for cutting or milling a window orlongitudinal section of the casing;

Figure 2 is a sectional view of the casing or pipe milling tool of thisinvention, illustrating the details thereof when the cutter knives arein a retracted position,

Figure 3 is a view similar to Figure 2, but illustrating the position ofthe cutter knives and the other parts of the tool after the knives havebeen pivoted to their extended position,

Figure 4 is a horizontal sectional view taken on line 4-4 of Figure 3and illustrates particularly the construction of the valve of the cuttertool, and

Figure 5 is a horizontal sectional view taken on line 5-5 of Figure 3and illustrates particularly the pivotal connection of the cutter knivesto the tool body or housing.

In the drawings the letter A designates generally the pipe or casingmilling tool of this invention which includes .a body or housing 10which is suspended from and supported by a support pipe or drill pipe P.The connection of the housing 10 to the support pipe P can be by theconventional tool joint or by the use of an adapter 11, a portion ofwhich is shown in Figure 2, such adapter 11 having connection with thesupport pipe P. Within the bore 19:: of the body or housing 10, there islocated a piston or fluid-actuated member 12 which co-acts with cutterknives 14 which are pivotally connected to the body or housing 10,whereby upon downward movement of the piston 12 the cutter knife orknives 14 are pivoted radially outwardly for cutting through a casing orpipe C and for thereafter milling out a window or longitudinal section Win the casing or pipe C (Figure l). A valve member 15 is provided in thebore 10a of the housing 10 for closing a longitudinal passage or bore12a of the piston 12 durprovide an improved pipe or casing surfaced forcutting purposes.

ing the downward movement of the ting through the pipe or casing C. isadapted to be full fluid flow through the piston passage 12a after thepipe or casing C has been cut through and while the window orlongitudinal section W of the pipe or casing C is being cut or milled bythe knives 14, as will be explained.

The details of the casing milling'tool of this invention are illustratedin Figures 2-5, and therein it can be seen that the housing or body 10has a plurality of radial slots 17 in its side wall, with a knife 14being disposed in each of such slots 17. Each knife 14 is pivoted to thehousing 10 by a pivot pin 18 which extends through openings 18a forpivotal movement of each knife from a retracted substantially verticalposition (Figure 2) to an extended substantially horizontal position(Figure 3). Each cutter knife 14 has a downwardly extending or outercutting edge 19 and a laterally extending or lower cutting edge 20, eachof such edges 19 and 20 preferably being hard The downwardly extendisprovided for cutting piston 12 while cut- The valve member 15 ing orouter cutting edge 19 unseated from the piston 12 to permit through thepipe or casing C as the cutter knife 14 is pivoted outwardly duringrotation of the tool A, while the lower or lateral cutting edge isprovided for cutting or milling the casing or pipe C which is beneaththe cutter knives 14 after they have been extended to the position shownin Figure 3. It will be observed thateach cutter knife 14 has arectangular recess 21 at its lower end which provides a reducedthickness at the tapered cutting edges 1.9 and 20. The upper portion ofthe cutter 14 is designated by the numeral 22 and is of the full widthof the. cutter to provide sufficient rigidity for the knife during itscutting action. Each knife 14 has an inner projection or lug 24 whichextends into the bore 10a of the housing or body 10 and co-acts with thepiston12.

For co-acting with the lugs 24 topivot the cutter knives 14, there isprovided on the external surface of the piston 12 an annular recess 25whereby an upper radially extending shoulder 26 is formed on the piston12 for contact with the lugs 24 as the piston 12 moves downwardlyrelative to the piston or body 19. The lower wall of the recess 25 formsa lower radially extending shoulder 27 which merges with afrusto-conieal section 28. When the cutters 14 have been extended to theposition shown in Figure 3, an upward movement of the piston 12 relativeto the housing 10 causes an engagementof the lower shoulder 27 with theprojections or lugs 24 to pivot the cutter knives 14 downwardly to aretracted position (Figure 2). The piston 12. is maintained in theretracted position and is returned to such retracted position by a coilspring 29 disposed below a lower shoulder 37a of an enlarged head 37 atthe upper end of the piston 12 and an inwardly extending ledge shoulder30 in the housing 10. The spring 29 has only sufficient strength tosupport the weight of the piston 12 and connected parts so that whenrnud pressure is applied to force the piston 12 downwardly, the force ofthe spring 29 is overcome. Upward movement of the piston 12 is limitedby the engagement of the lugs 24 with an inclined surface 32 in the boreof the housing 10 and contact of the frustoconical section 28 on thepiston 12 with the, lower edge of each of the cutters 14. Downwardmovement of the piston, 12 is limited by the contact of the lower end ofthe piston 12 with the upper end of a stop pipe 33 disposed on ashoulder 23 internally of a coil spring 31, which surrounds the stop 33and is confined between the lower end ofthe piston 12 and the shoulder23. The downward stop provided by the stop pipe 33 prevents the piston12. from moving so far downwardly that it would shear the pivot pins 18.The spring 31 isof a greater strength than the upper spring- 29 and issufi'icicntly strong to continuously resist downward movement of thepiston when mud pressure is applied thereabove; such resistance ofspring 31 prevents longitudinal vibration or chatter of the piston 12 asit is lowered to extend the knives 14 and also assures that all of theknives 14 apply substantially the same cutting force.

The piston 12 moves longitudinally in the housing 10 with the bore 10aserving as a piston chamber. Fluid seals are provided by O-rings 35 and36 mounted in grooves at the upper enlarged end 37 of the piston 12 andan O-ring 38 disposed near the lower end of the piston 12 below thefrusto-conical section 28. A radial port 10b is provided in the sidewall of the body 10 to permit ingress and egress of well fluid into thebore 10a during longitudinal movement of the piston 12.

The valve member 15 which is disposed above the piston in the bore 10aof the housing 10 is formed with a central circular plug section 40which has extending radially therefrom a plurality of radial guide legs.41, which legs 41 form the appearance of a Y as seen from the top of thetool (Figure 4). The longitudinal spaces 42 between each of the legs 41forms openings or passages for fluid flow through the valve, member 15.Theplug section 40 extends downwardly below the lower surfaces of thelegs 41 and forms a tapered valve seating surface 40a for seating upon asimilarly tapered valve seat 45 at the upper end of the longitudinalpassage or bore 12a of the piston 12. An orifice 46 which is of a verysmall diameter in comparison to the diameter of the longitudinal passage12a is provided in the valve 15, and it extends through the center ofthe central plug section 40 to establish fluid communicationbetween thearea above the valve 15 and the fluid passage 12. This fluidcommunication through the orifice 46 will exist even if the valveseating surface 49a is seated on the valve seat 45 to otherwise closethe longitudinal passage 12a.

Upward movement of the valve member 15 is limited by an internallydisposed stop shoulder 11a formed by the lower end of the adapter 11 orany similar section which connects with the support pipe P. When thecutter knives 14 are fully retracted and the piston 12 is in its extremeupper position (Figure 2) the valve member 15 will normally rest on thetop of the piston 12 with the valve seating surface 40a seating on thevalve seat 45 to substantially close the passage 12a. In the event thata fluid pressure is exerted upwardly through the tool by the, loweringof a tool into the well casing, for example, such pressure will actupwardly through the passage 12a and move the valve member 15 upwardlywith the limit of upward movement thereof being the stop shoulder 11a.

Downward movement of the valve member 15 is limited by an internalannular shoulder 58 in the upper portion of the bore of the housing 10.The shoulder 50 is so positioned that its stops the downward movement ofthe valve member 15 prior to the time that the lower end of the piston12- seats upon the upper end of the stop pipe 33, thereby permitting thepiston 12 to move downwardly relative to the valve member 15 to on seatthe valve seating surface 40a from the valve seat 45. This permits fluidfrom the support pipe P to pass through the spaces or openings 42between the radial guide legs 41 and then downwardly into thelongitudinal passage 12a. It is believed evident that the flow throughthe passage 12a with the valve member 15 unseated is much greater thanwhen the orifice 46 is the only fluid inlet to the passage from abovethe valve member 15; thus, with the valve member 15 unseatcd. a maximumof fluid can be supplied downwardly to the tool A and upwardly into thecasing so as to remove the cuttings during the milling out of the windowW in the casing C and to prevent any bridging of the formation F intothe casing C during the milling operation.

In the operation of the casing milling tool A of this invention, thetool is lowered into the casing to be out upon a support pipe P whichcan be conventional drill pipe, and as the tool is lowered into thecasing C the well fluid which is already in the casing can move upwardlyinto the tool through the open tail pipe P or theopen end of the tool itsuch tail pipe P is not used, and thence upwardly through thelongitudinal passage 12a to move the valve member 15 upwardly to unseatsame, and to permit fluid to enter the support pipe l. Thus, during thelowering of the tool into the casing, there is an automatic equalizationof fluid pressures interiorly and exteriorly of the tool. and itssupport pipe. with the amount of fill-up with the well fluid beingdetermined by the amount of well fluid in the casing C. This isaparticular advantage over the previously known tools since it avoids thenecessity for filling the drill pipe or support pipe P with liquid asthe tool is lowered into the casing, and therefore it avoids thestopping of the lowering of, the tool for such filling as is necessarywith the previous devices. Therefore, by reason of this construction thetool can be lowered into the well casing without. stopping its loweringmovement, and the fluid pressure interiorly and exteriorly of the toolis automatically equalized.

After the tool has been lowered to the point at which it is desired tocut through the casing or pipe C in the extended position,

well bore, fluid under pressure is applied downwardly through thesupport pipe P from the surface of the well, which fluid pressure actsupon the valve member 15 to urge it downwardly. Since the valve member15 is seated on the top of the piston 12 and substantially closes thelongitudinal passage 12a in the piston 12, the fluid pressure serves tomove the valve member 15 and the piston 12 downwardly together. Whilethe fluid pressure is being applied to move the valve member 15 and thepiston 12 downwardly, the support pipe P is rotated by an conventionalmeans at the surface of the well so that as the cutter knives 14 aremoved radially outwardly into engagement with the interior of the pipeor casing C, the rotation of the knives provides a cutting action on thecasing or well pipe C. As the cutting through of the well pipe or casingC progresses, the fluid pressure continues to pivot the cutter knives 14radially outwardly toward the fully extended position (Figure 3), andsuch action continues until the casing or Well pipe C is cut all of theway through, Just prior to the time that the cutter knives 14 reachtheir fully the valve member 15 is stopped in its downward movement bythe stop shoulder 50 so that the fluid pressure then forces the piston12 downwardly relative to the valve member 15 and unseats the seatingsurface 40a from the valve seat 45, whereby the fluid under pressurethen can pass through the opening 42 into longitudinal passage 12a. Thisprovides for circulation of fluid through and around the tool to etfectthe removal of the cuttings and also prevents bridging of the formationacross the interior of the casing after the pipe or casing C has beencut through The cutter knives 14 may be maintained in theirsubstantially horizontal extended position shown in Figure 3 to effectthe milling out of the casing C by the application of a predeterminedamount of fluid pressure through the support pipe P, or by imposing theweight of the drill pipe on the tool so that the contact of the lowercutting edge 29 with the upper edge of the portion of casing which isbeneath the knives 14 urges such knives to the position shown in Figure3. If desired, both the fluid pressure acting on the piston 12 and theweight of the support pipe P may be utilized to hold the cutter knivesextended.

With the cutter knives 14 thus held extended in a substantiallyhorizontal position and resting upon theupper edge of the portion of thecasing beneath the cutters 14, the rotation of the tool by the rotatingmeans at the surface of the well will cause the lower cutting surfaces20 to mill or cut the casing as the tool is lowered. The length ofwindow or longitudinal section W which is cut in the casing C will, ofcourse, depend upon the purpose of such window. The Window orlongitudinal section W in the casing C may be desired for setting awhipstock and directing a drill bit into the formation through thewindow, or for the production through the formation adjacent the window,as well as other operations.

As pointed out previously, during such milling operation in cutting thewindow or longitudinal section in the casing C, a suflicient amount ofdrilling fluid or mud can be circulated through the spaces or openings42 and into the longitudinal passage 12a and thence downwardly and outthrough the open end of the tool and upwardly into the casing C toprevent the cuttings from collecting and interfering'with the cuttingoperation and to prevent the formation from bridging or falling into thecasing.

After the longitudinal sectionor window W' is cut in the casing C, thefluid pressure can be released from above the valve member 15 and thereturn spring 30 will move the piston 12 upwardly to again seat with thevalve member 3.5 to close the passage 12a and to retract the cutters 14,whereby the tool can be removed from the casing C or can be moved toanother position for cutting.

V 8 V In some instances it may be desirable to locate couplings in thewell pipe or casing C prior to the cutting operation. This is vital inmaking measurements for opening a sand section in the formation or ininstances where directional drilling couplings are utilized. Thesecouplings can be located by applying a fluid pressure to-the valvemember 15 and the piston 12 through the support pipe P to move theknives 14 outwardly into the recess at the coupling. When the knivesmove into the recess, the downward movement of the tool will beprevented, and this can further be checked by continuing the lowering ofthe tool until the Weight indicator shows that the device is beingsupported on the knives in the coupling recess. Having located thecoupling, then the position at which the cutting is to be performed islocated and the knives are retracted and the tool is lowered to theposition in the casing C with respect to the located coupling at whichit is desired to cut through the casing.

It will be evident from the foregoing description that the casingmilling tool of this invention provides a structure wherein suflicientfluid pressure can be exerted on the knives for cutting through the wellcasing, while sufficient fluid or mud circulation can be obtained at thecutter knives during the milling out of the window or longitudinalsection of the casing. Additionally, the tool can be lowered into thewell Without stopping such lowering to fill the drill pipe in order toequalize the pressure on the interior of the drill pipe with that on theexterior in the casing. Another advantage which should be pointed out isthat the device may be cleared of any debris or foreign articles whichmay enter and plug the lower end of the tool during the cutting throughand milling out operations. With this tool the fluid circulation can bereversed by forcing fluid under pressure, such as drilling mud,downwardly through the casing and thence upwardly through thelongitudinal passage 12a to dislodge any debris and foreign articles inthe lower end of the tool. Then as the tool is raised in the casing toremove the tool therefrom, the fluid in the tool can pass through theorifice 46 and passage 12a as the tool is raised so that it is notnecessary to pull the tool while it is completely full of mud. In priortools, when they became plugged up with debris or foreign articles, thepipe string supporting the tool had to be pulled full of mud whichnecessitated a much greater lifting force and a loss of the drillingmud.

It might also be pointed out that each of the cutting knives of thisinvention has both an outer cutting edge and a lower cutting edge whichare hard surfaced with a material such as diamond, so that if the knivesare displaced at the initial cut due to a shifting of the pipe, thecutting edges will always be able to re-engage the pipe and cut thesame.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction may be made, within the scope of the appended claims,without departing from the spirit of the invention.

What is claimed is:

1. In a casing milling tool adapted to be rotated for cutting through acasing or pipe and for thereafter milling a longitudinal section of thecasing, a housing having an axial bore, a fluid-actuated piston in saidbore adapted to move longitudinally therein, a cutter knife pivotallymounted on said housing, means on said piston and said knife forpivoting said knife from a retracted substantially vertical position toan extended substantially horizontal position upon downward movement ofsaid piston relative to said housing, said piston having a longitudinalpassage therethrough communicating with the bore of said housing, valvemeans movable independently of the piston and operable by the fluidpressure acting on oppo-' site sides thereof for substantially closingsaid passage while. moving said piston downwardly to pivot said cutteroutwardly for cutting through the pipe or casing, and

means within the housing engageable with the valve means to open saidpassage after said pipe or casing is cut through whereby sufficientfluid circulation can be maintained downwardly through the tool andupwardly into the pipe or casing to wash away cuttings and the likeencountered while milling out the longitudinal section of the pipe orcasing.

2. The structure set forth in claim 1, including a support pipe fromwhich said housing is suspended, and means to rotate said support pipeto impart rotation to said tool, said knife being maintained in extendedposition on the upper end of the casing or pipe beneath the cutter knifeby imposing the weight of the support pipe on the tool,

3. The structure set forth in claim 1, wherein said cutter knife has adownwardly directed cutting for ting through the casing or pipe, and alaterally direct l cutting edge for engagement with the upper end of thecasing or pipe beneath the cutter knife for milling out a longitudinalsection of the casing or pipe as the knife is rotated and forceddownwardly.

4. A pipe or casing milling tool including, a tubular body, a cutterknife mounted on the body for movement from a retracted position to anextended cutting position,

a piston slidably mounted within the body between limits therein andmovable downwardly by the application of fluid pressure from above, saidpiston having means thereon co-acting with said cutter knife for movingsaid knife to its extended position when the piston is moved downwardlywithin the body, said piston having a longitudinal passage therethroughwhich when open permits a circulation of fluid in either directionthrough the piston and body, a valve member movable independently of thepiston by the pressures acting thereacross and adapted to co-act withthe passage for controlling the flow through the passage, means withinthe tubular body engageable by the valve for limiting movement of thevalve so that said valve member is movable between limits with respectto the body and with respect to the piston whereby the passage throughthe piston is controlled by the valve member in accordance with theposition of the piston and also in accordance with the pressures actingon the valve member.

5. A pipe or casing milling tool including, a tubular body, a cutterknife mounted on the body for movement from a retracted position to anextended cutting position, a piston slidably mounted within the bodybetween limits therein and movable downwardly by the application offluid pressure from above, said piston having means thereon co-actingwith said cutter knife for moving said knife to its extended positionwhen the piston is moved downwardly within the body, said piston havinga longitudinal passage therethrough which when open permits acirculation of fluid in either direction through the piston and body, avalve member movable independently of the piston by the pressures actingthereacross and adapted to co-act with the passage for controlling theflow through the passage, a lower stop element within the bodyengageable by the valve member to limit downward movement of said memberand located so that downward movement of the valve member is halted toopen the passage through the piston before the piston has completed itsfull downward travel and prior to the time the cutter knife has beenfully extended, and an upper stop element within the body alsoengageable by the valve member for limiting its upward movement, saidupper stop member being so located that when the piston is at itsuppermost limit of travel the valve member may undergo sufficientmovement to open the passage through the piston.

6. A pipe or casing milling tool including, a tubular body, a cutterknife mounted on the body for movement from a retracted position to anextended cutting position, a piston slidably mounted within thebodybetween limits therein and movable downwardly by the application offluid pressure from above, saidipistonhaving means thereon coacting withsaid cutter knife for moving said knife. to its extended position whenthe piston is moved downwardly within the body, said piston having alongitudinal passage therethrough which when open permits a circulationof fluid in either. direction through the piston and body, a valvemember movable, independently of the piston by the pressures actingthereacross and adapted to coact with the passage for con trolling theflow through the passage, said valve member being movable between limitswith respect to the body and with respect to the piston whereby thepassage through the piston is controlled by the valve member inaccordance with the position of the piston and also in accordance withthe pressures, acting on the valve member, said valve member having anorifice therein which permits limited flow past said valve when thevalve is in a position closing the passage through the piston.

7. A pipe and milling tool as set forth in claim 5, wherein the valvemember has an orifice therein which permits limited flow past the valvewhen the valve is in a position closing the passage through the piston.

8. A pipe or casing milling tool including, a tubular body, a cutterknife mounted on the body for movement from a retracted position to anextended cutting position, a piston slidably mounted within the bodybetween limits therein and movable downwardly by the application offluid pressure from above, said piston having means thereon co-actingwith said cutter knife for moving said knife to its extended positionwhen the piston is moved downwardly within the body, said piston havinga longitudinal passage therethrough which when open permits acirculation of fluid in either direction through the piston and body, avalve seat at the upper end of the passage, a valve member movablewithin the body above the piston and adapted to co-act with the valveseat to control flow through the passage, said valve member beingmovable by pressures acting on opposite sides thereof, a lower stopelement within the body engageable by the valve member for limitingdownward movement of the valve member, said stop element being solocated with respect to the travel of the. piston that downward movementof said valve is halted prior to the time the piston completes itsdownward travel whereby during the latter portion of the pistonsdownward travel the valve member is unseated and the piston passage isopen to permit free circulation of fluid downwardly through the pistonand body.

9. A pipe or casing cutter as set forth in claim 8, together with an.upper stop element within the body engageable by the valve member forlimiting its upward movement in the body, said upper stop element beingso located with respect to the piston travel that said valve member maymove upwardly away from the piston when the piston is at its upper limitof travel whereby the pressure. below the valve member may act to openthe passage when the piston is in its uppermost position.

10. A pipe or casing cutter as set forth in claim 8, together with anupper stop element within the body engageable by the valve member forlimiting its upward movement in the body, said upper stop element beingso located with respect to the piston travel that said valve member may.move upwardly away from the piston when the piston is at its upper limitof travel whereby the pressure below the valve member may act to openthe passage when the piston is in its uppermost position, said valvemember having a reduced size orifice therein permitting flow past saidmember when the same is in a position closing the piston passage.

11. A pipe or casing milling tool as set forth in claim 5, together.with a spring means associated with the piston for normally urgingsaidpiston upwardly within the body.

12. A pipe or casing milling tool as set forth in claim 8, together witha spring means associated with the piston fornormally urging said pistonupwardly within the body.

(References on following page) References Cited in the file of thispatent 2,299,528 UNITED STATES PATENTS 2,482,674 Re. 21,824 Lowrey June10, 1941 1,632,015 Ventresca June 14, 1927 2,218,766 Parker Oct. 22,1940 5 412923 Conner Oct. 20, 1942 Kriegel Sept. 20, 19 49 FOREIGNPATENTS Germany Apr. 9, 1925

